There is a plethora of references (both patents and literature articles) dealing with the formation of diacids, one of the most important being adipic acid. Adipic acid is used to produce Nylon 66 fibers and resins, polyesters, polyurethanes, and miscellaneous other compounds.
There are different processes of manufacturing adipic acid. The conventional process involves a first step of oxidizing cyclohexane with oxygen to a mixture of cyclohexanone and cyclohexanol (KA mixture), and then oxidation of the KA mixture with nitric acid to adipic acid. Other processes include, among others, the "Hydroperoxide Process", the "Boric Acid Process", and the "Direct Synthesis Process", which involves direct oxidation of cyclohexane to adipic acid with oxygen in the presence of solvents, catalysts, and promoters.
The Direct Synthesis Process has been given attention for a long time. However, to this date it has found little commercial success. One of the reasons is that although it looks very simple at first glance, it is extremely complex in reality. Due to this complexity, one can find strikingly conflicting results, comments, and views in different references.
It is well known that after a reaction has taken place according to the Direct Synthesis, a mixture of two liquid phases is present at ambient temperature, along with a solid phase mainly consisting of adipic acid. The two liquid phases have been called the "Polar Phase" and the "Non-Polar Phase". However, no attention has been paid so far to the importance of the two phases, except for separating the adipic acid from the "Polar Phase" and recycling these phases to the reactor partially or totally with or without further treatment.
It is also important to note that most, if not all, studies on the Direct Oxidation have been conducted in a batch mode, literally or for all practical purposes.
There is a plethora of references dealing with oxidation of organic compounds to produce acids, such as, for example, adipic acid and/or intermediate products, such as for example cyclohexanone, cyclohexanol, cyclohexylhydroperoxide, etc.
The following references, among the plethora of others, may be considered as representative of oxidation processes relative to the preparation of diacids and intermediate products.
U.S. Pat. No. 5,463,119 (Kollar) discloses a process for the oxidative preparation of C.sub.5 -C.sub.8 aliphatic dibasic acids by
(1) reacting, PA1 (2) removing the aliphatic dibasic acid; and PA1 (3) recycling intermediates, post oxidation components, and derivatives thereof remaining after removal of the aliphatic dibasic acid into the oxidation reaction. PA1 (1) reacting, at a cycloaliphatic hydrocarbon conversion level of between about 7% and about 30%, PA1 (2) isolating the C5-C8 aliphatic dibasic acid. PA1 (a) reacting at least part of the hydrocarbon in the mixture being at the first temperature and at the first pressure with a gaseous oxidant to form at least part of the dibasic acid; PA1 (b) lowering the first temperature to a second temperature, while maintaining one-liquid-phase at the second temperature; and PA1 (d) removing at least part of the formed acid; PA1 a first reaction chamber; PA1 first temperature control means connected to the first reaction chamber for controlling the temperature in said first reaction chamber; PA1 first pressure control means connected to the reaction chamber for controlling the pressure in said first reaction chamber; PA1 first hydrocarbon feeding means connected to the first reaction chamber for feeding hydrocarbon into said first reaction chamber; PA1 first gaseous oxidant feeding means connected to the first reaction chamber for feeding gaseous oxidant into said first reaction chamber; PA1 a second chamber connected to the first reaction chamber; PA1 second temperature control means connected to the second chamber for controlling the temperature in said second chamber; PA1 second pressure control means connected to the second chamber for controlling the pressure in said second chamber; PA1 second phase control means for maintaining the mixture in the second chamber in a single liquid phase; and PA1 separating means connected to or being part of the second chamber for separating at least partially the dibasic acid from the mixture. PA1 a first reaction chamber; PA1 first temperature control means connected to the first reaction chamber for controlling the temperature in said first reaction chamber; PA1 first pressure control means connected to the reaction chamber for controlling the pressure in said first reaction chamber; PA1 first hydrocarbon feeding means connected to the first reaction chamber for feeding hydrocarbon into said first reaction chamber; PA1 first gaseous oxidant feeding means connected to the first reaction chamber for feeding gaseous oxidant into said first reaction chamber; PA1 a first intermediate chamber communicating with the first reaction chamber; PA1 first intermediate temperature control means connected to the first intermediate chamber for controlling the temperature in said first intermediate chamber; PA1 first intermediate pressure control means connected to the intermediate chamber for controlling the pressure in said first intermediate chamber; PA1 first intermediate external heating means for providing thermal energy to matter inside the first intermediate chamber; PA1 an intermediate condenser connected to the first intermediate chamber; PA1 a second chamber connected to the first intermediate chamber; PA1 second temperature control means connected to the second chamber for controlling the temperature in said second chamber; PA1 second pressure control means connected to the second chamber for controlling the pressure in said second chamber; PA1 a controller for controlling miscellaneous parameters in the chambers in a manner that in the second chamber there is a single liquid phase. PA1 separating means connected to or being part of the second chamber for separating at least partially the dibasic acid from the mixture. PA1 a second intermediate chamber between the first intermediate chamber and the second chamber; PA1 second intermediate external cooling means for removing thermal energy from matter inside the first intermediate chamber;
(a) at least one saturated cycloaliphatic hydrocarbon having from 5 to 8 ring carbon atoms in the liquid phase and PA2 (b) an excess of oxygen gas or an oxygen-containing gas in the presence of PA2 (c) a solvent comprising an organic acid containing only primary and/or secondary hydrogen atoms and PA2 (d) at least about 0.002 mole per 1000 grams of reaction mixture of a polyvalent heavy metal catalyst; PA2 (a) at least one saturated cycloaliphatic hydrocarbon having from 5 to 8 ring carbon atoms in the liquid phase and PA2 (b) an excess of oxygen gas or an oxygen containing gas mixture in the presence of PA2 (c) less than 1.5 moles of a solvent per mole of cycloaliphatic hydrocarbon (a), wherein said solvent comprises an organic acid containing only primary and/or secondary hydrogen atoms and PA2 (d) at least about 0.002 mole per 1000 grams of reaction mixture of a polyvalent heavy metal catalyst; and
U.S. Pat. No. 5,374,767 (Drinkard et al) discloses formation of cyclohexyladipates in a staged reactor, e.g. a reactive distillation column. A mixture containing a major amount of benzene and a minor amount of cyclohexene is fed to the lower portion of the reaction zone and adipic acid is fed to the upper portion of the reaction zone, cyclohexyladipates are formed and removed from the lower portion of the reaction zone and benzene is removed from the upper portion of the reaction zone. The reaction zone also contains an acid catalyst.
U.S. Pat. No. 5,321,157 (Kollar) discloses a process for the preparation of C.sub.5 -C.sub.8 aliphatic dibasic acids through oxidation of corresponding saturated cycloaliphatic hydrocarbons by
U.S. Pat. No. 5,221,800 (Park et al) discloses a process for the manufacture of adipic acid. In this process, cyclohexane is oxidized in an aliphatic monobasic acid solvent in the presence of a soluble cobalt salt wherein water is continuously or intermittently added to the reaction system after the initiation of oxidation of cyclohexane as indicated by a suitable means of detection, and wherein the reaction is conducted at a temperature of about 50.degree. C. to about 150.degree. C. at an oxygen partial pressure of about 50 to 420 pounds per square inch absolute.
U.S. Pat. No. 3,987,100 (Barnette et al.) describes a process of oxidizing cyclohexane to produce cyclohexanone and cyclohexanol, said process comprising contacting a stream of liquid cyclohexane with oxygen in each of at least three successive oxidation stages by introducing into each stage a mixture of gases comprising molecular oxygen and an inert gas.
U.S. Pat. No. 3,957,876 (Rapoport et al.) describes a process for the preparation of cyclohexyl hydroperoxide substantially free of other peroxides by oxidation of cyclohexane containing a cyclohexane soluble cobalt salt in a zoned oxidation process in which an oxygen containing gas is fed to each zone in the oxidation section in an amount in excess of that which will react under the conditions of that zone.
U.S. Pat. No. 3,932,513 (Russell) discloses the oxidation of cyclohexane with molecular oxygen in a series of reaction zones, with vaporization of cyclohexane from the last reactor effluent and parallel distribution of this cyclohexane vapor among the series of reaction zones.
U.S. Pat. No. 3,530,185 (Pugi) discloses a process for manufacturing precursors of adipic acid by oxidation with an oxygen-containing inert gas which process is conducted in at least three successive oxidation stages by passing a stream of liquid cyclohexane maintained at a temperature in the range of 140.degree. to 200.degree. C. and a pressure in the range of 50 to 350 p.s.i.g. through each successive oxidation stage and by introducing a mixture of gases containing oxygen in each oxidation stage in an amount such that substantially all of the oxygen introduced into each stage is consumed in that stage thereafter causing the residual inert gases to pass countercurrent into the stream of liquid during the passage of the stream through said stages.
U.S. Pat. No. 3,515,751 (Oberster et al) discloses a process for the production of epsilon-hydroxycaproic acid in which cyclohexane is oxidized by liquid phase air oxidation in the presence of a catalytic amount of a lower aliphatic carboxylic acid and a catalytic amount of a peroxide under certain reaction conditions so that most of the oxidation products are found in a second, heavy liquid layer, and are directed to the production of epsilon-hydroxycaproic acid.
U.S. Pat. No. 3,361,806 (Lidov et al) discloses a process for the production of adipic acid by the further oxidation of the products of oxidation of cyclohexane after separation of cyclohexane from the oxidation mixture, and more particularly to stage wise oxidation of the cyclohexane to give high yields of adipic acid precursors and also to provide a low enough concentration of oxygen in the vent gas so that the latter is not a combustible mixture.
U.S. Pat. No. 3,234,271 (Barker et al) discloses a process for the production of adipic acid by the two-step oxidation of cyclohexane with oxygen. In a preferred embodiment, mixtures comprising cyclohexanone and cyclohexanol are oxidized. In another embodiment, the process involves the production of adipic acid from cyclohexane by oxidation thereof, separation of cyclohexane from the oxidation mixture and recycle thereof, and further oxidation of the other products of oxidation.
U.S. Pat. No. 3,231,608 (Kollar) discloses a process for the preparation of aliphatic dibasic acids from saturated cyclic hydrocarbons having from 4 to 8 cyclic carbon atoms per molecule in the presence of a solvent which comprises an aliphatic monobasic acid which contains only primary and secondary hydrogen atoms and a catalyst comprising a cobalt salt of an organic acid, and in which process the molar ratio of said solvent to said saturated cyclic hydrocarbon is between 1.5:1 and 7:1, and in which process the molar ratio of said catalyst to to said saturated cyclic hydrocarbon is at least 5 millimoles per mole.
U.S. Pat. No. 3,161,603 (Leyshon et al) discloses a process for recovering the copper-vanadium catalyst from the waste liquors obtained in the manufacture of adipic acid by the nitric acid oxidation of cyclohexanol and/or cyclohexanone.
U.S. Pat. No. 2,565,087 (Porter et al) discloses the oxidation of cycloaliphatic hydrocarbons in the liquid phase with a gas containing molecular oxygen and in the presence of about 10% water to produce two phases and avoid formation of esters.
U.S. Pat. No. 2,557,282 (Hamblet et al) discloses production of adipic acid and related aliphatic dibasic acids; more particularly to the production of adipic acid by the direct oxidation of cyclohexane.
U.S. Pat. No. 2,439,513 (Hamblet et al) discloses the production of adipic acid and related aliphatic dibasic acids and more particularly to the production of adipic acid by the oxidation of cyclohexane.
U.S. Pat. No. 2,223,494 (Loder et al) discloses the oxidation of cyclic saturated hydrocarbons and more particularly to the production of cyclic alcohols and cyclic ketones by oxidation of cyclic saturated hydrocarbons with an oxygen-containing gas.
U.S. Pat. No. 2,223,493 (Loder et al) discloses the production of aliphatic dibasic acids and more particularly to the production of aliphatic dibasic acids by oxidation of cyclic saturated hydrocarbons with an oxygen-containing gas.
None of the above references, or any other references known to the inventors disclose, suggest or imply, singly or in combination, oxidation reactions to intermediate oxidation products under phase-controlled conditions subject to the intricate and critical controls and requirements of the instant invention as described and claimed.
Our U.S. Pat. Nos. 5,580,531, 5,558,842, 5,502,245, and our co-pending application Ser. Nos. 08/477,195 (filed Jun. 7, 1995), 08/587,967 (filed Jan. 17, 1996), and 08/620,974 (filed Mar. 25, 1996), all of which are incorporated herein by reference, describe methods and apparatuses relative to controlling reactions in atomized liquids. Our co-pending, U.S. patent application Ser. No. 08/812,847 of Mark W. Dassel, Eustathios Vassiliou, David C. DeCoster, Ader M. Rostami, and Sharon M. Aldrich, titled "Methods and Devices for Controlling the Reaction Rate of a Hydrocarbon to an Acid by Making Phase-related Adjustments", filed on Mar. 6, 1997, is also incorporated herein by reference.